Plastic lenses are lightweight, less fragile and dyeable, as compared with inorganic lenses. For these reasons, plastic lenses have rapidly spread in optical elements such as eyeglass lenses and camera lenses. A variety of resins for eyeglass lenses have heretofore been developed and used. Representative examples among them are allyl resins obtained from diethylene glycol bis-allyl carbonates and diallyl isophthalates, (meth)acrylic resins obtained from (meth)acrylates, and polythiourethane resins obtained from isocyanates and thiols.
Among them, a polythiourethane-based resin obtained from isophorone diisocyanate is lightweight and also exhibits a high refractive index, low dispersion and excellent transparency, and therefore it is very useful as a material for plastic lenses.
Patent Document 1 discloses that a polythiourethane-based plastic lens having excellent impact resistance, a high refractive index, low dispersion, and a low specific gravity is obtained by addition of a specific third component to isophorone diisocyanate and 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane.
Patent Document 2 discloses that a lens having good optical properties, a low specific gravity, and excellent impact resistance is obtained from a composition containing dicyclohexylmethane diisocyanate and 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane.
Patent Document 3 discloses the use of a heat-treated phosphoric acid ester in order to prevent white turbidity, since when formulating a catalyst master batch into which a phosphoric acid ester-based releasing agent is blended, there may be a case where the master batch becomes cloudy due to the lot number of the phosphoric acid ester-based release agent.
Patent Document 4 discloses a method of inhibiting the modification of a polyisocyanate compound by mixing the polyisocyanate compound with an acidic phosphoric acid ester, and then adding a polythiol and an alkyltin halide polymerization catalyst to prepare a composition, since the addition of the alkyltin halide to the polyisocyanate compound leads to some cases where the polyisocyanate may be modified by moisture, when obtaining a polythiourethane-based plastic lens obtained from a polyisocyanate and a polythiol.
Patent Document 5 discloses a process for producing a polyurethane lens, including step of casting and polymerizing a mixture containing a polyisocyanate, a polythiol, and a specific phosphoric acid diester into a mold for producing a plastic lens. Example 3 describes obtaining a polyurethane lens from a composition containing a mixture of isophorone diisocyanate, pentaerythritol tetrakismercaptopropionate, monobutoxyethyl acid phosphate and di(butoxyethyl) acid phosphate, and dimethyltin dichloride. The Examples therein have confirmed the impact resistance of the thus obtained polyurethane lens by a method that meets the US FDA standard: Drop Ball Test: test using a 16.3 g steel ball dropping from a height of 127 cm onto a lens surface).
Patent Documents 6 to 9 disclose a process for producing a polyurethane lens, including step of preparing a polyisocyanate compound and two or more polythiol compounds having a different reaction rate with the polyisocyanate compound, step of adding a predetermined alkyltin halide compound to the polyisocyanate compound, and step of mixing and reacting the polyisocyanate compound and the two or more polythiol compounds with the predetermined alkyltin halide compound to obtain a polyurethane lens.
The Examples in these documents disclose obtaining a polyurethane lens from compositions containing a mixture of isophorone diisocyanate, pentaerythritol tetrakismercaptoacetate, dimercaptomethyl dithiane, dimethyltin dichloride, dibutoxyethyl acid phosphate, and butoxyethyl acid phosphate.